Directional drilling is a process in which the direction in which a wellbore is formed is controlled during drilling. Directional drilling permits wellbores to access specific targets where it would be difficult or impossible to use vertical drilling equipment, such as underground reserves that lie directly beneath surface areas under municipalities, lakes, or other natural or manmade features. Directional drilling also allows multiple wellheads to be grouped together, with the wellbores extending away from the group in various directions underground such as on an off shore platform. Directional drilling is also used to form a near horizontal portion of a wellbore that intersects a greater portion of a petroleum reservoir than a vertical wellbore would penetrate thereby increasing the drainage efficiency of the wellbore.
One general type of directional drilling involves the use of a downhole mud motor having a bent motor housing coupled to the drill string. The drill bit at the end of the drill string may be rotated either by rotating the entire drill string from the surface, or by rotating just the drill bit using the mud motor housing. When rotating the entire drill string from the surface, the bent motor housing rotates along with the rest of the drill string, to drill a nominally straight wellbore section. By ceasing rotation from the surface and rotating the drill bit using just the downhole mud motor, a deviated section is formed at an angle determined by the bend in the motor housing (a process known as “sliding”).
Another type of directional drilling involves the use of a rotary steerable drilling system that controls an azimuthal direction and/or degree of deflection while the entire drill string is rotated continuously. Rotary steerable drilling systems typically involve the use of an actuation mechanism that actively causes the drill bit to deviate from the current path using either a “point the bit” or “push the bit” mechanism. In a “point the bit” system, the actuation mechanism is controlled to deflect and orient the drill bit to a desired position by bending the drill bit drive shaft within the body of the rotary steerable assembly. As a result, the drill bit tilts and deviates with respect to the borehole axis. In a “push the bit” system, the actuation mechanism is instead controlled to selectively push the drill string against the wall of the borehole, thereby offsetting the drill bit with respect to the borehole axis. Yet another directional drilling technique, generally referred to as the “push to point,” encompasses a combination of the “point the bit” and “push the bit” methods.